There are a variety of different IC manufacturing processes, including complementary metal oxide semiconductor (CMOS), Bipolar, and Bipolar CMOS (BiCMOS). Every IC has specified operating and environmental conditions, including maximum operating voltages, to ensure reliability. Processes and techniques used when fabricating ICs to ensure reliability include the use of dielectric isolation such as dielectric trenches and buried oxide (BOX) operable to isolate components from one another.
Dielectric isolation is a well-known technique for fabricating high voltage devices in integrated circuits. The technique involves growing a silicon dioxide insulating layer on a handle wafer, then bonding a silicon wafer onto the oxide layer to form a Silicon-On-Insulator (SOI) wafer structure. The handle is a silicon substrate over which the buried oxide (BOX) and thinner top silicon layer are deposited. The technique further involves etching trenches in the silicon substrate down to the buried oxide (BOX) layer, the trenches thus separating islands of silicon referred to as tubs. The trenches are then further oxidized and backfilled. The tubs are thus electrically isolated from each other by the insulating trenches and BOX layer. Regardless of the process used, a maximum operating voltage is typically specified for an IC component.
No products or methods exist for increasing maximum IC component operating voltages other than designing components capable of operating at higher voltages. Typically, a series connection is used for component level design when higher voltages are required. What is desired is an integrated circuit including therein at least one component operable to withstand very high voltages.
In one simple example, a simple resistor divider capable of dividing voltages above 1000V may be required. Referring to circuit 100 of FIG. 1, if the very high voltage (VHV) is 1000 volts then VHV/100 is approximately 10 volts. In the circuit 100 of FIG. 1, the challenge is designing and fabricating the 30 MegOhm resistor 101 such that it withstands voltages greater than 1000 volts. Using the components seen in circuit 100 of FIG. 1, the fabrication process only allows for 320 volt maximum potential between resistor (polysilicon) electrodes and tub and 650 volts between tubs and 700 volts between tubs and handle.